1. Field of the invention
This invention relates to a loop taker and a sewing machine.
2. Description of the Prior Art
A typical prior art arrangement is shown in FIG. 1. A horizontal axis full rotary loop taker has a cup shaped hook body 1 which supports a bobbin case holder 2 in position. In the bobbin case holder 2 there is mounted a bobbin case 5 shown by a phantom line for housing a bobbin 4 on which a bobbin thread 3 is wound. The hook body 1 is fixedly mounted on a horizontal rotary shaft 6 for rotation therewith. A needle 7, as arrows 8 show, is reciprocatingly movable up and down, the lowermost point of the path of its movement being shown by reference numeral 9. The rotation axis of the bobbin 4 is on a straight line coaxially or in parallel with the rotary shaft 6.
FIG. 2 is a sectional view of the hook body 1 in which the bobbin case holder 2 is housed. A bobbin case holder rib 10 formed on the outer periphery of the holder 2 is fitted in a hook groove 11 formed in the hook body 1.
A loop 13 of a needle thread 12 is seized by a loop seizing point 17, and as the hook body 1 rotates, the thread 12 progresses from its loop condition as shown in FIG. 3(1) into a loop state as shown in FIG. 3(2). The needle thread 12 passes itself through the loop while being in contact with a lower portion 14a of the bottom 14 of the bobbin case holder 2, and then it slides around the bottom 14 of the holder 2 as shown in FIG. 3(3).
In such a prior art arrangement, if the quantity of the bobbin thread wound on the bobbin 4 is to be increased, it is necessary either to (a) increase the outer diameter D of the bobbin 4 or to (b) increase the axial length H of the bobbin 4.
(a) In the case where the outer diameter D of the bobbin 4 is increased, the hook groove 11 in the hook body 1 and the rib 10 on the holder 2 are necessarily diametrically enlarged. Therefore, if the rotational speed of the hook body 1 is constant, the peripheral speed of the hook groove 11 will be increased. Accordingly, the frictional force between the hook groove 11 and the rib 10 will be increased. As a consequence, there will be an increase in the amount of heat released.
As a result of the increase in frictional force, considerable tension will be exerted on the needle thread 12 when the thread 12 passes through an abutment surface between a rotation restraining notch 15 of the bobbin case holder 2 and a stopper member which is in engagement with the notch 15. Thus, stitches are unfavorably tightened, which fact is likely to lead to incidental knotted needle thread or looping.
(b) For the purpose of increasing the axial length H of the bobbin 4, two approaches may be considered: (b1) the bobbin 4 is extended toward the open end side (rightward in FIG.1) of the bobbin case holder 2, and (b2) the bottom 14 of the bobbin case holder 2 is extended leftward in FIG. 1, while the bobbin 4 is extended toward the bottom 14 side.
In the case where the (b1) approach of extending the bobbin 4 toward the open end side of the case holder 2 is adopted, the trouble is that in the up and down reciprocating movement of the needle 7, the needle point will be lowered radially inwardly of the radially outer side of the bobbin thread 3 wound on the bobbin 4, when it is lowered to the lowermost point 9 of needle movement, so that the needle 7 will run into the bobbin thread 3 wound on the bobbin 4, whereby breakage may be caused to the bobbin thread 3 wound on the bobbin 4.
In the case where the (b2) approach of extending the bottom 14 of the bobbin case holder 2 leftward in FIG. 1 is adopted, as FIG. 4 shows, the resulting configuration is such that the prior arrangement of them bottom 14 shown by a phantom line is extended leftward in FIG. 4. As such, the needle thread 12 is caught in the lower portion 14a of the bottom 14 of the bobbin case holder 2 and thus thread passing is rendered impossible, with the result that sewing is made impossible.